Method for improving the efficiency of heat transfer in a coal fired furnace

ABSTRACT

An additive having as components, at least three metal oxides selected from iron, manganese, cobalt, and copper oxide, may be added to coal to reduce the brightness of ash produced therewith. Further, the additive serves to increase the heat transfer efficiency of furnaces.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. provisional patentapplication Ser. No. 61/267,712 filed Dec. 8, 2009 the disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to coal fired furnace systems. The presentinvention particularly relates to coal-fired furnaces including systemsfor adding additives to coal.

2. Background of the Art

Petrochemical plants, oil refineries, power generation stations, and thelike; all utilize furnaces for heat generation. For centuries, man hasrelied upon the combustion of combustible materials, such as coal andwood, to provide heat energy. One of the most common methods forharnessing this heat energy is to use the heat energy to generate steamor heat other types of fluids.

Over the years, different types of furnaces or boilers have beendeveloped for the combustion of coal, wood, and other combustiblematerials. In the late 1940's and early 1950's, there was a largedecline in the demand for commercial and industrial solid fuel-firedsystems due to the wide-spread availability of relatively cheap oil andnatural gas sources. Thus, the oil and gas-fired systems substantiallyreplaced the coal-fired systems until the gas and oil petroleum-basedfuels became less plentiful during the 1970's. The petroleum shortageexperienced during the 1970's and the very high prices of the late2000's have made coal-fired and other solid fuel-fired systems veryattractive once again.

In recent years, considerable emphasis has been given to solid fuelresearch, particularly in the area of burning solid fuels such as coaland wood without excessive pollutant emissions and with increased heattransfer efficiency. As the costs of oil and gas continue to escalate,the utilization of solid fuel systems (such as coal-fired systems) willcontinue to increase.

SUMMARY OF THE INVENTION

In one aspect, the invention is a process for treating coal to increaseheat transfer efficiency in coal burning furnaces comprising: contactingthe coal with an additive prior to or concurrent with combustion of thecoal wherein: the additive functions to increase radiant heat adsorptionof coal ash; and the additive does not include a fluxing agent.

In another aspect, the invention is a process for treating coal toincrease heat transfer efficiency in coal burning furnaces includingcontacting the coal with an additive wherein the additive is a pigmentcomprising at least 3 oxides selected from Fe, Cu, Co, and Mn oxides.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee. The advantages and further aspects of thedisclosure will be readily appreciated by those of ordinary skill in theart as the same becomes better understood by reference to the followingdetailed description when considered in conjunction with theaccompanying figures:

FIG. 1 is a photograph of ash treated with 0.01% additive;

FIG. 2 is a photograph of ash treated with 0.02% additive;

FIG. 3 is a photograph of ash treated with 0.05% additive; and

FIG. 4 is a photograph of an untreated sample of ash.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one embodiment, the invention is a process for treating coal toincrease heat transfer efficiency in coal burning furnaces. One type ofsuch a furnace, the stoker-fired furnace, was developed to burnrelatively large particles of coal, up to about 1.5 inches in diameter.Later, another type of furnace, the pulverized coal-fired furnace, wasdeveloped for burning much smaller coal particles, e.g., where about 70%of the coal particles pass through a 200 mesh screen. Pulverizedcoal-fired furnaces have large steam generating capacities and are thustypically used in steam generating installations where at least 500,000pounds of steam per hour are required. For example, the electric powergenerating industry has been one of the largest users of pulverizedcoal-fired furnaces, since large amounts of steam are required for theproduction of electric energy.

With either type of furnace, the coal added to the furnace combusts toproduce heat. In some furnaces, the coal that does not instantly combustfalls upon a grate on which the burning fuel bed resides. The gratemoves, in some embodiments, at a very slow rate, e.g., from about 5 to40 feet per hour, and eventually dumps the combustion by-products(namely, residual ash) into an ash pit or some other receptacle.Alternatively, the grate may be stationary but have the capability ofbeing dumped at periodic intervals to remove the bed of accumulated ash.In some furnaces, the burning fuel bed is sluiced out.

One reason for the popularity of the spreader-stoker-fired furnace isits high superficial grate heat release rates of up to 750,000BTU/hr-ft² and its low inertia due to nearly instantaneous fuel ignitionupon increased firing rate. This high superficial grate heat release isobtained because of the relatively uniform distribution of the coalparticles in the burning fuel bed on the grate, the relatively smalldepth of the layer of coal particles on the grate, and the intensecombustion during the suspension phase above the burning fuel bed. Thelow inertia allows the spreader-stoker-fired furnace to respond rapidlyto load fluctuations in steam demand, and hence in boiler load, whichare common in industrial applications.

In the practice of the method of the application, the coal to be burnedmay be treated with an additive. In one embodiment, the additive is apigment including oxides of iron, copper, cobalt and manganese. Thispigment interacts with coal ash to darken the ash.

By darkening the coal ash, heat transfer is improved within the furnace.While not wishing to be bound by any theory, it is believed that radiantheat is more efficiently absorbed by the ash clinging to the walls ofthe furnace when the ash is dark. Especially when that surface is a heatexchanger tube, the radiant energy may be transferred to the heattransfer medium along with the normal convected heat resulting in moreheat reaching the heat transfer medium and thereby improving theefficiency of the furnace.

The additive of the disclosure does not include a fluxing agent. Forexample, there is no need to add a fluxing agent such as a borate.Fluxing agents in general and borate fluxing agents in specific areknown to those of ordinary skill in the art. One advantage of theadditive of the disclosure is that it stays with the ash without theneed for a fluxing agent. Other pigments, if not affixed to coal ash,may be problematic. For example, some pigments may travel up the stackof a coal furnace and cause opacity problems. Other pigments may presentdisposal problems.

While the additive of the disclosure may be used with any type of coal,it is desirably utilized with coal that has high levels of calcium. Suchcoal produces a very light colored ash and even a very small amount ofadditive may provide for a significant improvement in heat transferefficiency.

The additive of the invention is an inorganic pigment that includes atleast 3 of the oxides of copper, iron, cobalt, and manganese. In someembodiments all 4 metals may be present. The additive may, in someembodiments, have from about 15 to about 60% by weight (as metal) copperoxide; from about 20 to about 70% by weight (as metal) manganese oxide;from about 20 to about 70% by weight cobalt; and from about 5 to about30% by weight (as metal) iron oxide. In other embodiments, the additivemay have from about 25 to about 45% by weight (as metal) copper oxide;from about 35 to about 60% by weight (as metal) manganese oxide; fromabout 35 to about 60% by weight (as metal) cobalt; and from about 10 toabout 25% by weight (as metal) iron oxide.

The additive may be added to coal or it may be added directly to afurnace as coal is being fed as fuel. In one embodiment, the additive issprayed onto coal as a liquid prior to it being pulverized. In one suchembodiment, a nozzle is used to perform the spraying. In anotherembodiment, the additive is sprayed onto coal as a liquid after it hasbeen pulverized. In still another embodiment, the additive is introducedinto coal as a solid. Another embodiment of the method of the disclosureincludes introducing the additive as a solid prior to the coal beingpulverized. The additive may be introduced into coal or a furnace usingany method known to be useful to those of ordinary skill in the art.

The methods of the disclosure may be used advantageously to improvepower plant operations. In some applications, more power may be producedper unit of coal. In other applications, the need for removing soot fromthe inside of a furnace may be reduced. In still other applications,both of these advantages may be noted.

EXAMPLES

The following examples are provided to illustrate the present invention.The examples are not intended to limit the scope of the presentinvention and they should not be so interpreted. Amounts are in weightparts or weight percentages unless otherwise indicated.

Example 1

An inorganic pigment including iron, manganese, and copper oxides;available from the FERRO Corporation under the trade designationF-6331-2 is used to darken coal ash. A high calcium lignite coal isadmixed with the additive at a concentration of 0.01%. The ash is burnedand then scanned. The resulting scan is evaluated using an HSB (Hue,Saturation, and Brightness) model. The HSB model represents points in anRGB color model that attempt to describe perceptual color relationshipsmore accurately than RGB, while remaining computationally simple. HSBallows colors to be interpreted as tints, tones and shades. Byconverting the samples into this electronic color model it is possibleto measure the difference in actual brightness, while keeping hue andsaturation independent. The scan may be seen below in FIG. 1. The sampleis measured and has a brightness of 44%

Example 2

Example 1 is repeated substantially identically except that 0.02% ofadditive is used. The scan may be seen below at FIG. 2. The brightnessis measured as 37%.

Example 3

Example 1 is repeated substantially identically except that 0.05% ofadditive is used. The scan may be seen below at FIG. 3. The brightnessis measured as 27%.

Comparative Example Control

Example 1 is repeated substantially identically except that no additiveis used. The scan may be seen below at FIG. 4. The brightness ismeasured as 68%.

TABLE Sample ID [Additive in wt. %] Brightness % % Change Ex 1 0.01 4435.3 Ex 2 0.02 37 45.6 Ex 3 0.05 27 60.3 Control — 68 —

Hypothetical Example

A power plant driven by a coal fired furnace is operated using untreatedcoal. Variables recorded during the operations include the rate at whichcoal is introduced into the furnace, megawatts of power produced, andthe frequency of “soot-blows.” This latter term refers to the processwhere soot deposited on the furnace tubes is blown from the furnaceusing a blower. After the power plant is operating at a steady load, theadditive of Example 1 is introduced on to the coal being fed into thefurnace by spraying a solution/dispersion of the additive onto the coal.After the introduction of the additive into the furnace, and allowingthe power plant to return to operation at a steady load, it is notedthat more megawatts of power is produced per unit of coal, and fewersoot-blows are required per shift.

1. A process for treating coal to increase heat transfer efficiency incoal burning furnaces comprising: contacting the coal with an additiveprior to or concurrent with combustion of the coal wherein: the additivefunctions to increase radiant heat adsorption of coal ash as comparedwith an otherwise identical process absent the additive; and theadditive does not include a fluxing agent.
 2. The process of claim 1wherein the additive is a pigment comprising at least 3 oxides selectedfrom Fe, Cu, Co, and Mn oxides.
 3. The process of claim 2 wherein thepigment comprises Fe, Cu and Mn oxides.
 4. The process of claim 3wherein the pigment comprises from about 15 to about 60% by weight (asmetal) copper oxide; from about 20 to about 70% by weight (as metal)manganese oxide; and from about 5 to about 30% by weight (as metal) ironoxide.
 5. The process of claim 4 wherein the pigment comprises fromabout 25 to about 45% by weight (as metal) copper oxide; from about 35to about 60% by weight (as metal) manganese oxide; and from about 10 toabout 25% by weight (as metal) iron oxide.
 6. The process of claim 2wherein the pigment comprises Fe, Cu and Co oxides.
 7. The process ofclaim 6 wherein the pigment comprises from about 15 to about 60% byweight (as metal) copper oxide; from about 20 to about 70% by weight (asmetal) cobalt oxide; and from about 5 to about 30% by weight (as metal)iron oxide.
 8. The process of claim 7 wherein the pigment comprises fromabout 25 to about 45% by weight (as metal) copper oxide; from about 35to about 60% by weight (as metal) cobalt oxide; and from about 10 toabout 25% by weight (as metal) iron oxide.
 9. The process of claim 1wherein the additive is a pigment comprising Fe, Cu, Co, and Mn oxides.10. The process of claim 9 wherein the pigment comprises from about 15to about 60% by weight (as metal) copper oxide; from about 20 to about70% by weight (as metal) manganese oxide; from about XX to about YY % byweight (as metal) cobalt; and from about 5 to about 30% by weight (asmetal) iron oxide.
 11. The process of claim 10 wherein the pigmentcomprises from about 25 to about 45% by weight (as metal) copper oxide;from about 35 to about 60% by weight (as metal) manganese oxide; fromabout XX2 to about YY2% by weight (as metal) cobalt; and from about 10to about 25% by weight (as metal) iron oxide.
 12. The process of claim 1wherein the additive is introduced to the coal prior to combustion. 13.The process of claim 12 wherein the additive is sprayed onto the coal.14. The process of claim 13 wherein the process further comprisespulverizing the coal, and the additive is sprayed onto the coal prior topulverizing.
 15. The process of claim 13 wherein the process furthercomprises pulverizing the coal, and the additive is sprayed onto thecoal after or concurrently with pulverization.
 16. The process of claim12 wherein the additive is admixed with the coal as a solid.
 17. Theprocess of claim 16 wherein the additive is admixed with the coal priorto or concurrently with pulverization.
 18. The process of claim 1wherein the additive is introduced to the coal concurrently withcombustion.
 19. The process of claim 19 wherein the additive is sprayedinto the furnace.
 20. A process for treating coal to increase heattransfer efficiency in coal burning furnaces comprising: contacting thecoal with an additive prior to or concurrent with combustion of the coalwherein: the additive functions to increase radiant heat adsorption ofcoal ash; the additive does not include a fluxing agent; and theadditive is a pigment comprising at least 3 oxides selected from Fe, Cu,Co, and Mn oxides.